/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.i18n;

import java.util.Locale;
import java.util.TimeZone;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.context.i18n.LocaleContext;
import org.springframework.context.i18n.TimeZoneAwareLocaleContext;
import org.springframework.lang.Nullable;
import org.springframework.web.util.WebUtils;

/**
 * {@link org.springframework.web.servlet.LocaleResolver} implementation that
 * uses a locale attribute in the user's session in case of a custom setting,
 * with a fallback to the specified default locale or the request's
 * accept-header locale.
 *
 * <p>This is most appropriate if the application needs user sessions anyway,
 * i.e. when the {@code HttpSession} does not have to be created just for storing
 * the user's locale. The session may optionally contain an associated time zone
 * attribute as well; alternatively, you may specify a default time zone.
 *
 * <p>Custom controllers can override the user's locale and time zone by calling
 * {@code #setLocale(Context)} on the resolver, e.g. responding to a locale change
 * request. As a more convenient alternative, consider using
 * {@link org.springframework.web.servlet.support.RequestContext#changeLocale}.
 *
 * <p>In contrast to {@link CookieLocaleResolver}, this strategy stores locally
 * chosen locale settings in the Servlet container's {@code HttpSession}. As a
 * consequence, those settings are just temporary for each session and therefore
 * lost when each session terminates.
 *
 * <p>Note that there is no direct relationship with external session management
 * mechanisms such as the "Spring Session" project. This {@code LocaleResolver}
 * will simply evaluate and modify corresponding {@code HttpSession} attributes
 * against the current {@code HttpServletRequest}.
 *
 * @author Juergen Hoeller
 * @see #setDefaultLocale
 * @see #setDefaultTimeZone
 * @since 27.02.2003
 */
public class SessionLocaleResolver extends AbstractLocaleContextResolver {

    /**
     * Name of the session attribute that holds the Locale.
     * Only used internally by this implementation.
     * <p>Use {@code RequestContext(Utils).getLocale()}
     * to retrieve the current locale in controllers or views.
     *
     * @see org.springframework.web.servlet.support.RequestContext#getLocale
     * @see org.springframework.web.servlet.support.RequestContextUtils#getLocale
     */
    public static final String LOCALE_SESSION_ATTRIBUTE_NAME = SessionLocaleResolver.class.getName() + ".LOCALE";

    /**
     * Name of the session attribute that holds the TimeZone.
     * Only used internally by this implementation.
     * <p>Use {@code RequestContext(Utils).getTimeZone()}
     * to retrieve the current time zone in controllers or views.
     *
     * @see org.springframework.web.servlet.support.RequestContext#getTimeZone
     * @see org.springframework.web.servlet.support.RequestContextUtils#getTimeZone
     */
    public static final String TIME_ZONE_SESSION_ATTRIBUTE_NAME = SessionLocaleResolver.class.getName() + ".TIME_ZONE";


    private String localeAttributeName = LOCALE_SESSION_ATTRIBUTE_NAME;

    private String timeZoneAttributeName = TIME_ZONE_SESSION_ATTRIBUTE_NAME;


    /**
     * Specify the name of the corresponding attribute in the {@code HttpSession},
     * holding the current {@link Locale} value.
     * <p>The default is an internal {@link #LOCALE_SESSION_ATTRIBUTE_NAME}.
     *
     * @since 4.3.8
     */
    public void setLocaleAttributeName(String localeAttributeName) {
        this.localeAttributeName = localeAttributeName;
    }

    /**
     * Specify the name of the corresponding attribute in the {@code HttpSession},
     * holding the current {@link TimeZone} value.
     * <p>The default is an internal {@link #TIME_ZONE_SESSION_ATTRIBUTE_NAME}.
     *
     * @since 4.3.8
     */
    public void setTimeZoneAttributeName(String timeZoneAttributeName) {
        this.timeZoneAttributeName = timeZoneAttributeName;
    }


    @Override
    public Locale resolveLocale(HttpServletRequest request) {
        Locale locale = (Locale) WebUtils.getSessionAttribute(request, this.localeAttributeName);
        if (locale == null) {
            locale = determineDefaultLocale(request);
        }
        return locale;
    }

    @Override
    public LocaleContext resolveLocaleContext(final HttpServletRequest request) {
        return new TimeZoneAwareLocaleContext() {
            @Override
            public Locale getLocale() {
                Locale locale = (Locale) WebUtils.getSessionAttribute(request, localeAttributeName);
                if (locale == null) {
                    locale = determineDefaultLocale(request);
                }
                return locale;
            }

            @Override
            @Nullable
            public TimeZone getTimeZone() {
                TimeZone timeZone = (TimeZone) WebUtils.getSessionAttribute(request, timeZoneAttributeName);
                if (timeZone == null) {
                    timeZone = determineDefaultTimeZone(request);
                }
                return timeZone;
            }
        };
    }

    @Override
    public void setLocaleContext(HttpServletRequest request, @Nullable HttpServletResponse response,
                                 @Nullable LocaleContext localeContext) {

        Locale locale = null;
        TimeZone timeZone = null;
        if (localeContext != null) {
            locale = localeContext.getLocale();
            if (localeContext instanceof TimeZoneAwareLocaleContext) {
                timeZone = ((TimeZoneAwareLocaleContext) localeContext).getTimeZone();
            }
        }
        WebUtils.setSessionAttribute(request, this.localeAttributeName, locale);
        WebUtils.setSessionAttribute(request, this.timeZoneAttributeName, timeZone);
    }


    /**
     * Determine the default locale for the given request,
     * Called if no Locale session attribute has been found.
     * <p>The default implementation returns the specified default locale,
     * if any, else falls back to the request's accept-header locale.
     *
     * @param request the request to resolve the locale for
     * @return the default locale (never {@code null})
     * @see #setDefaultLocale
     * @see javax.servlet.http.HttpServletRequest#getLocale()
     */
    protected Locale determineDefaultLocale(HttpServletRequest request) {
        Locale defaultLocale = getDefaultLocale();
        if (defaultLocale == null) {
            defaultLocale = request.getLocale();
        }
        return defaultLocale;
    }

    /**
     * Determine the default time zone for the given request,
     * Called if no TimeZone session attribute has been found.
     * <p>The default implementation returns the specified default time zone,
     * if any, or {@code null} otherwise.
     *
     * @param request the request to resolve the time zone for
     * @return the default time zone (or {@code null} if none defined)
     * @see #setDefaultTimeZone
     */
    @Nullable
    protected TimeZone determineDefaultTimeZone(HttpServletRequest request) {
        return getDefaultTimeZone();
    }

}
